1. Field of the Invention
The present invention relates to a gas discharge apparatus, and more particularly to a gas discharge apparatus and a plasma display panel that is adaptive for reducing a discharge voltage as well as increasing its brightness and luminescence efficiency.
2. Description of the Related Art
Generally, a gas discharge apparatus is made in a tube or panel shape to be used as a lighting light source. Recently, a plasma display panel (hereinafter, referred to as “PDP”), which displays a picture by use of gas discharge principle, is put on the market.
The PDP has attracted attention as a large sized flat panel display, and it makes a phosphorus emit light by an ultraviolet ray of 147 nm which is generated upon the discharging of an inert mixture gas (or discharge gas) such as He+Xe, He+Ne+Xe or Ne+Xe, thereby displaying a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Particularly, a three electrode AC surface discharge PDP has advantages of a low voltage driving and a long life span in that it can lower a voltage required for a discharge using wall charges accumulated on the surface thereof during the discharge and protect the electrodes from a sputtering generated by the discharge.
FIG. 1 is a diagram representing a discharge cell of a related art three electrode AC surface discharge PDP.
Referring to FIG. 1, a discharge cell of the three electrode AC surface discharge PDP includes a scan electrode Y and a sustain electrode Z formed on an upper substrate 10, and an address electrode X formed on a lower substrate 18. Each of the scan electrode Y and the sustain electrode Z includes transparent electrodes 12Y, 12Z and metal bus electrodes 13Y, 13Z of which each has a narrower line width than the transparent electrode and is formed at one side edge of the transparent electrode.
The transparent electrodes 12Y, 12Z are formed of indium tin oxide ITO on the upper substrate 10 in the related art. The metal bus electrodes 13Y, 13Z are formed of a metal such as chrome Cr on the transparent electrodes 12Y; 12Z to act to reduce a voltage drop which is caused by the transparent electrodes 12Y, 12Z of high resistance. A dielectric layer 14 and a passivation film 16 are deposited on the upper substrate 10 where the scan electrode Y and the sustain electrode Z are formed in parallel. A wall charge generated upon a plasma discharge is accumulated in an upper dielectric layer 14. The passivation film 16 prevents the loss of the upper dielectric layer 14 from the sputtering caused by ions generated upon the plasma discharge and increases the emission efficiency of secondary electrons. The passivation film 16 is of magnesium oxide MgO in the related art.
A lower dielectric layer 22 is formed on the lower substrate 18 where the address electrode X is formed, and a phosphorus layer 26 is spread over the surface of barrier ribs 24 and the lower dielectric layer 22. The address electrode X is formed in a direction that it crosses the scan electrode Y and the sustain electrode Z. The barrier ribs 24 are formed in a stripe or lattice shape to prevent an ultraviolet ray and a visible ray, which are generated by the discharge, from leaking into adjacent discharge cells. The phosphorus layer 26 is excited by the ultraviolet ray, which is generated upon the plasma discharge, to generate any one of red, green and blue visible rays. An inert mixture gas is injected into a discharge space provided between the upper/lower substrate 10, 18 and the barrier ribs 24.
In order to realize the gray level of a picture, the PDP is time-dividedly driven by dividing one frame into several sub-fields that have the number of their light emissions different from one another. Each sub field can be divided into a reset period to initialize a full screen, an address period to select scan lines and select cells from the selected scan lines, and a sustain period to realize gray levels in accordance with the number of discharges.
Herein, the reset period is divided into a setup period when a rising ramp waveform is supplied and a setdown period when a falling ramp waveform is supplied. For example, in the event of displaying a picture with 256 gray levels; the frame period (16.67 ms) corresponding to 1/60 second as in FIG. 2 is divided into 8 sub-fields (SF1 to SF8). Each of the 8 sub-fields (SF1 to SF8), as described above, is divided into the reset period, the address period and the sustain period. The reset period and the address period of each sub-field are the same for each sub-field, while the sustain period increases at the rate of 2n (n=0,1,2,3,4,5,6,7) in each sub-field.
FIG. 3 is a waveform representing a driving method of a related art PDP.
Referring to FIG. 3, the related art PDP is divided into the reset period to initialize the whole screen, the address period to select the cell and the sustain period to keep the discharge of the selected cell, to be driven.
In the reset period, a rising ramp waveform Ramp-up that rises to a peak voltage Vp is simultaneously applied to all the scan electrodes Y in a the setup period. The rising ramp waveform Ramp-up causes a weak discharge to be generated within the cellw of the whole screen, thereby generating wall charges within the cells. The rising ramp waveform Ramp-up like this remains at the peak voltage Vp for a designated time after rising to the peak voltage Vp.
In the setdown period, a falling ramp waveform Ramp-down that falls from a positive voltage, which is lower than the peak voltage Vp, to a negative voltage −Vr is simultaneously applied to the scan electrodes Y. The falling ramp wave form Ramp-down causes a weak erasure discharge to be generated within the cells, thus eliminating unnecessary charges among the space charges and the wall charges generated by the setup discharge and causing the necessary wall charges to remain behind uniformly, wherein the necessary wall charges are required for the address discharge within the cells of the whole screen.
In the address period, a negative scan pulse Scan is sequentially applied to the scan electrodes Y, and at the same time, a positive data pulse Data is applied to the address electrodes X. The voltage difference of the data pulse Data from the scan pulse Scan is added to the wall voltage which is generated during the reset period, to generate an address discharge within the cell to which the data pulse Data is applied. The address discharge causes the wall charges generated within the selected cells, wherein the wall charges are necessary for the cell discharge of the sustain period.
On the other hand, a positive DC voltage of sustain voltage level Vs is supplied to the sustain electrodes Z during the setdown period and the address period.
In the sustain period, the sustain pulse Vs is alternately applied to the scan electrodes Y and the sustain electrodes Z. Then, in the cell selected by the address discharge, the sustain discharge is generated in a surface discharge form between the scan electrode Y and the sustain electrode Y whenever the sustain pulse Vs is applied as the wall voltage within the cell is added to the sustain pulse Vs. Lastly, after completion of the sustain discharge, an erasure ramp waveform Erase with small pulse width is supplied t the sustain electrode Z to erase the wall charges within the cell.
On the other hand, in the related art, there is proposed a method of increasing the brightness by increasing the mixture ratio of Xe in the discharge gas, which is sealed within the PDP, to 4%˜6%. To describe this more specifically, in case of a conventional PDP which is used commercially, it has an efficiency of about 1.0˜1.2 lm/W on the basis of the PDP module. However, in the PDP, if the Xe ratio is increased to 4˜6%, it has an efficiency of not more than about 1.5 lm/W. Accordingly, it is possible to display an image having higher brightness and luminescence efficiency in the PDP where Xe of 4%˜6% is included in the discharge gas than a low density Xe PDP.
As another method for improving the brightness and the luminescence efficiency, there is proposed a long gap PDP method that the distance between the scan electrode Y and the sustain electrode Z formed on the upper substrate is made to be long in a 60˜80 μm level.
However, the high density Xe PDP or the long gap PDP has disadvantage that a discharge firing voltage or a discharge voltage becomes higher in comparison with the low density Xe or show gap PDP. In other words, if Xe of high density is injected into the PDP or the gap between the upper plate electrodes is broadened, then the discharge generation probability becomes low by the Xe component or the gap between the electrodes. Accordingly, in order to generate the discharge stably, a discharge voltage having high voltage value has to be applied. Further, in the high density Xe PDP or the long gap PDP, the discharge voltage where the discharge starts becomes higher, thus there is a problem that power is consumed as high as that. Because high power consumption is required like this, in order to drive the high density Xe PDP or the long gap PDP smoothly, it is required to use expensive drive circuit devices, thus there are problems that the manufacturing cost increases and the reactive power increases due to high power consumption.